Exposure of Equal-Channel Angular Extruded Tungsten to Deuterium Plasma

Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluences of 3×10^24 D/m^2 and 1×10^25 D/m^2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy（SEM） and thermal desorption spectroscopy（TDS）.Sparse and small blisters（0.1 μm） were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at 220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.